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INLET
NOTE, SECOND AUTOMATIC VALVE OPERATOR AND SERVO PRESSURE REGULATOR
SHOWN OUTSIDE GAS CONTROL FOR EASE IN TRACING GAS FLOW.
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SLOW-OPENING GAS CONTROL HAS A GAS FLOW RESTRICTOR IN THIS PASSAGE.
12,3978
FIG. 13-POSITION OF GAS CONTROL COMPONENTS DURING BURNER ON CYCLE.
operator opens. Outlet pressure to the main burner in
creases gradually from O inches wc (0 kPa) to rated output
pressure within 3 to 6 seconds (for an 80,000 Btuh furnace
at 7 inches wc (1.8 kPa] inlet pressure and 3.5 inches wc
(0.9 kPa) outlet pressure).
Step-Opening Pressure Regulation (VR8304P)
Step-opening gas controls actually combine two pres
sure regulators, one for the low pressure and one for the
full-rate pressure. When the thermostat calls for heat, the
automatic operator valve disc opens. The low pressure
regulator maintains outlet pressure at the preset step rate
for several seconds. Then the regulator valve is forced full
open by the timing diaphragm, which is operated by bleed
gas. When the low pressure regulator is full open, the high
pressure regulator maintains the desired full-rate outlet
-
FIRE OR EXPLOSION HAZARD
CAN CAUSE PROPERTY DAMAGE, SEVERE
INJURY OR DEA TH
Do not disassemble the gas control; It contains
no replaceable components. Attempted disas
sembly or repair may damage the gas control.
13
pressure as described for the standard regulator.
The step model requires approximately 60 seconds to
reset once the main burner goes off. If it is re-energized
within 60 seconds, it may bypass or shorten the length of
the low pressure step. Theburner may relight atthe full flow
rate.
WHEN THE CALL FOR HEAT ENDS
When the call for heat ends, the first automatic valve
and the second automatic valve operator close, bypassing
the regulator(s) and shutting off the main burner and the
pilot gas flow. As pressure inside the gas control and
underneath the automatic valve diaphragm equalizes,
spring pressure closes the second automatic valve to
provide a second barrier to gas flow.
CAUTION
Do not apply a jumper across or short the valve coil
terminals. Doing so may burn out the heat anticipa
tor in the thermostat or damage the electronic mod
ule.
.-------IMPORTANT--------,
Allow 60 seconds after shutdown before re-energiz
ing step-opening model to ensure lightoff at step
pressure.
68-0108-1
